Accuracy of seven vapour intrusion algorithms for VOC in groundwater

Abstract

During the last decade, soil contamination with volatile organic contaminants (VOC) received special attention because of their potential to cause indoor air problems. Moreover, research has shown that people spend 64% to 94% of there time indoors; therefore, the indoor air quality is of a primary importance for exposure to VOC. Human health risks to VOC-in cases of soil contamination-are often dominated by the exposure route 'inhalation of indoor air'. Exposure is often a result of vapour transport from the soil or groundwater to the indoor air of the building. Within human health risk assessments, a variety of algorithms are available that calculate transfer of soil gas to the indoor air. These algorithms suffer from a relatively high uncertainty due to a lack of representation of spatial and temporal variability. For such an application, these algorithms need to be further verified empirically against field observations so that they can be sufficiently reliable for regulatory purposes. This paper presents the accuracy for seven algorithms by using observed and predicted soil and indoor air concentrations from three sites, where the groundwater had been contaminated with aromatic and chlorinated VOC. The algorithms for vapour intrusion that are frequently used in European countries were included in this study and were Vlier-Humaan (Flanders), CSoil (Netherlands), VolaSoil (Netherlands), Johnson & Ettinger (USA), Risc (United Kingdom), and the dilution factor (DF) algorithms from Sweden and Norway. Three sites were investigated in more detail and samples were taken synoptically from the groundwater, soil and indoor air on four occasions. On the petroleum sites, the aromatic hydrocarbons benzene, toluene, ethylbenzene and xylenes were analysed and, on the dry cleaning sites, the chlorinated hydrocarbons tetrachloroethylene, trichloroethylene and cis 1,2-dichloroethene. To increase spatial resolution, measurements in groundwater and soil air were taken in three different zones at each site, in the close proximity of or in the building. During sampling, several relevant soil properties were measured like the bulk density, water and air filled porosity, soil temperature and depth of the groundwater. Also, building properties like the dimensions of the building and the quality of the floor were registered. The seven algorithms were applied to compare that observed with the predicted concentrations in soil and indoor air. The groundwater concentrations were used as a source contamination. The results from the algorithms were compared by using performance criteria to assess the accuracy of each algorithm. All calculations are presented in a box plot that contains the predicted soil or indoor air versus the observed concentrations. Results from the applied criteria are presented for each algorithm. Differences between predictions and observations were up to three orders of magnitude and can be partially related to the amount of parameters included in each algorithm and the mathematical concept used. For example, the ...

Vapour intrusion from the vadose zone—seven algorithms compared

“…The results from the present study are in line with earlier testing of accurateness based on comparing predictions with observations (Johnson et al 2002;Tillman and Weaver 2006;Hers et al 2002Hers et al , 2003Huijsmans and Wezenbeek 1995;Van Wijnen and Lijzen 2006;Provoost et al 2009). Their results focussed however on one or several screening-level algorithms and were therefore not able to rank the algorithm according to their accuracy, except in Provoost et al (2009) where algorithms were ranked for vapour intrusion as a result of groundwater contamination.…”

“…These algorithms are frequently used by various countries within Europe for site-specific health risk assessment and/ or the derivation of soil screening levels. A short description of these algorithms and further references are given in Provoost et al (2009) and below an overview table with key references is presented (Table 1).…”

“…Researchers have suggested to use screening-level algorithms with site-specific data in order to evaluate them for the vapour intrusion pathway (Fitzpatrick and Fitzgerald 2002;Johnson et al 2002;Hers et al 2003;Huijsmans and Wezenbeek 1995;Tillman and Weaver 2006;van Wijnen and Lijzen 2006;Provoost et al 2009). Screening-level algorithms typically performed phase partitioning calculations to estimate the concentration of a particular contaminant in soil gas from its concentration in another phase (i.e.…”

Probabilistic Risk Assessment for Six Vapour Intrusion Algorithms

“… SFT dilution factor (Norway) (SFT, 1999), hereafter DF NO  Johnson and Ettinger model (United States) (Johnson, 2005), hereafter JEM  CSoil algorithm (Netherlands) (Brand, Otte, & Lijzen, 2007;Otte, Lijzen, Otte, Swartjes, & Versluijs, 2001)  VolaSoil algorithm (Netherlands) (Waitz, Freijer, Kreule, & Swartjes, 1996;van Wijnen & Lijzen, 2006;Bakker, Lijzen, & van Wijnen, 2008)  Vlier-Humaan algorithm (region Flanders in Belgium) (OVAM, 2004), hereafter Vl-H The background of each of the selected algorithms is described in Provoost et al (2010), and in more detail in Provoost et al (2008b, 2009) and McAlary et al (2011. An overview of the processes included in these algorithms is provided in Table 1.…”

“…The accuracy and conservatism of screening-level algorithms is objectified by calculating the Maximum relative Error (ME), Root Mean Squared Error (RMSE) and Coefficient of Residual Mass (CRM), as described by Loague and Green (1991), for the paired predicted and observed air concentrations. These criteria were applied in Provoost et al (2008bProvoost et al ( , 2009, and also in this study, for inter-algorithm comparison and provided a ranking of the algorithms as to their accuracy.…”